We have fabricated an encapsulated monolayer MoS 2 device with metallic ohmic contacts through a prepatterned hBN layer. In the bulk, we observe an electron mobility as high as 3000 cm 2 /Vs at a density of 7 × 10 12 cm −2 at a temperature of 1.7 K. Shubnikov-de Haas oscillations start at magnetic fields as low as 3.3 T. By realizing a single quantum dot gate structure on top of the hBN we are able to confine electrons in MoS 2 and observe the Coulomb blockade effect. By tuning the middle gate voltage we reach a double dot regime where we observe the standard honeycomb pattern in the charge stability diagram.Contrary to graphene, in monolayer molybdenum disulfide (MoS 2 ) inversion symmetry is broken. This, together with the presence of time-reversal symmetry, endows single layer MoS 2 with individually addressable valleys in momentum space at the K and K points in the first Brillouin zone. 1-4 This valley addressability facilitates the momentum state of electrons to be used for novel qubit architectures. Recent theoretical works have been exploring the possibility of using spin and valley states of gate-defined quantum dots in 2D MoS 2 as quantum bits. [5][6][7] In this manuscript, we describe the observation of Coulomb blockade in single and coupled dot in a high quality single layer MoS 2 . The high electronic quality of our monolayer MoS 2 results in the observation of Shubnikov-de Haas oscillations (SdHO) occurring at magnetic fields as low as 3.3 T. The 2DEG in the MoS 2 can be electrostatically depleted below the gate pattern with resistance values exceeding the resistance quantum h/e 2 by orders of magnitude. We observe Coulomb blockade resonances close to pinch-off indicating single electron tunneling in and out of the dot. By adjusting the gate voltages, we are able to tune the electrostatic landscape inside the dot and to form a double dot system within a single dot gate structure. [8][9][10][11] In Fig. 1(a), we show the schematic of a monolayer MoS 2 (∼ 0.7 nm thick) encapsulated between two hexagonal boron nitride (hBN) layers. The measured MoS 2 flake was exfoliated from natural bulk crystal (SPI supplies). The bottom hBN layer is ∼ 30 nm thick and works both as an atomically flat substrate and as a dielectric that isolates the MoS 2 from a graphite backgate. The graphite gate enables us to control electrostatically the electron density in MoS 2 with the voltage V bg . The layers thicknesses were determined by atomic force microscopy (AFM). The top hBN layer (∼50nm thick) has a) Electronic mail: pisonir@phys.ethz.ch been pre-patterned using E-beam lithography and reactive ion etching. 12 This enables us to evaporate metallic contacts (Ti/Au) on top of the MoS 2 layer where the hBN has been etched away, without exposing the channel region to organic residues remaining from the fabrication process. 13 Prior to metal evaporation, the heterostructure has been annealed in forming gas (Ar/H 2 ) at 300 • C for 30 minutes in order to remove most of the organic residues on top of the MoS 2 contact regions a...

The strong spin-orbit coupling and the broken inversion symmetry in monolayer transition metal dichalcogenides (TMDs) results in spin-valley coupled band structures. Such a band structure leads to novel applications in the fields of electronics and optoelectronics. Density functional theory calculations as well as optical experiments have focused on spin-valley coupling in the valence band. Here we present magnetotransport experiments on high-quality n-type monolayer molybdenum disulphide (MoS2) samples, displaying highly resolved Shubnikov-de Haas oscillations at magnetic fields as low as 2 T. We find the effective mass 0.7 me, about twice as large as theoretically predicted and almost independent of magnetic field and carrier density. We further detect the occupation of the second spin-orbit split band at an energy of about 15 meV, i.e. about a factor 5 larger than predicted. In addition, we demonstrate an intricate Landau level spectrum arising from a complex interplay between a density-dependent Zeeman splitting and spin and valley-split Landau levels. These observations, enabled by the high electronic quality of our samples, testify to the importance of interaction effects in the conduction band of monolayer MoS2.Monolayer transition metal dichalcogenides (TMDs) such as MoS 2 , MoSe 2 , WS 2 and WSe 2 are twodimensional (2D) semiconductors with band extrema at the corners (K, K -points) of the first Brillouin zone [1]. Due to the strong spin-orbit coupling the spin degeneracy in the K and K valleys is lifted, with opposite spin polarization normal to the layer plane in opposite valleys (see Fig. 2, inset). This peculiar band structure with coupled spin and valley degrees of freedom results in an anomalous Landau level (LL) structure [2][3][4]. Theoretical proposals predict the formation of LLs under the influence of a perpendicular magnetic field that are arranged differently from those in conventional semiconductor quantum wells and graphene [3]. Magnetotransport measurements have recently been performed in monolayer WSe 2 , MoSe 2 and bilayer MoS 2 revealing two-fold degenerate LLs, large effective masses and carrier density dependent Zeeman splitting [5][6][7][8][9]. Previous works on thicker MoS 2 , MoSe 2 and WSe 2 devices have measured the electron LLs structure at the Q and Q conduction band minima, showing the thickness dependence of the band structure in 2D TMDs [10,11]. Here we focus on single layer MoS 2 where for low electron densities electrons clearly reside at the K-K minima of the bandstructure.Here we report transport measurements in high mobility dual-gated monolayer MoS 2 under a perpendicular magnetic field. Our devices show ohmic contacts at temperatures as low as T ≈ 100 mK allowing us to uncover signatures of so far not reported rich interplay of strong spin-orbit coupling and electron-electron interactions. Shubnikov-de Haas (SdH) oscillations appear already at magnetic fields B ≈ 2 T at a temperature of T ≈ 100 mK. From the temperature dependence of the SdH oscillations we measure an...

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We demonstrate direct measurements of the spin-orbit interaction and Landé g factors in a semiconductor nanowire double quantum dot. The device is made from a single-crystal purephase InAs nanowire on top of an array of finger gates on a Si/SiO2 substrate and the measurements are performed in the Pauli spin-blockade regime. It is found that the double quantum dot exhibits a large singlet-triplet energy splitting of ΔST ~2.3 meV, a strong spinorbit interaction of ΔSO ~140 eV, and a large and strongly level-dependent Landé g factor of ~12.5. These results imply that single-crystal pure-phase InAs nanowires are desired semiconductor nanostructures for applications in quantum information technologies.

These authors contributed equally to this work. InSb is one of the promising candidates to realize a topological state through proximity induced superconductivity in a material with strong spin-orbit interactions. In two-dimensional systems, thin barriers are needed to allow strong coupling between superconductors and semiconductors. However, it is still challenging to obtain a high-quality InSb two-dimensional electron gas in quantum wells close to the surface. Here we report on a molecular beam epitaxy grown heterostructure of InSb quantum wells with substrate-side Si-doping and ultra-thin InAlSb (5 nm, 25 nm, and 50 nm) barriers to the surface. We demonstrate that the carrier densities in these quantum wells are gate-tunable and electron mobilities up to 350,000 cm 2 (Vs) −1 are extracted from magneto-transport measurements. Furthermore, from temperature-dependent magneto-resistance measurements, we extract an effective mass of 0.02 m 0 and find a Zeeman splitting compatible with the expected band edge g-factor.